The objective of the proposed research is to develop a host-mediated in vitro model for the identification of potential carcinogens. Neonatal rats will be injected for 3 days with a series of known procarcinogens and carcinogens. The rats will be killed on day 4, the livers removed, and epithelioid cell cultures will be prepared. The cultures will be examined for a) morphologic transformation, b) chromosomal changes, both qualitative and quantitative, c) soft agar growth, d) protease activity by the casein overlay techniques, e) their ability to produce tumors upon implantation into syngeneic newborn rats. In addition, the capacity of the cell lines to secrete the variants of alpha-fetoprotein, i.e., the concanavalin A-retained and non-retained proteins, will be examined by ConA-Sepharose chromatography; relationship between the ratio of these 2 variants and the ease of malignant transformation will be established. Their aryl hydrocarbon hydroxylase activity and metabolic spectrum after incubation with 3H-benzo(a)pyrene will be determined by spectrophotofluorimetric and high pressure liquid chromatographic techniques. The relationship of all these parameters to the production of malignant transformation will be established and the utility of this model as a means for identification of carcinogens will be verified.